diff --git a/composer.json b/composer.json
index 2ea6781..352f3c2 100644
--- a/composer.json
+++ b/composer.json
@@ -46,7 +46,7 @@
         "php-di/php-di": "^6.0"
     },
     "require-dev": {
-        "phpunit/phpunit": "^8",
+        "phpunit/phpunit": "^9",
         "phpdocumentor/phpdocumentor": "2.*",
         "evert/phpdoc-md": "0.2.0",
         "phly/changelog-generator": "^2.1"